The Botulinum toxins comprise a group of zinc-dependent endopeptidases. Seven immunotypes of Botulinum neurotoxins have been characterized, these are referred to, respectively, as immunotypes A, B, C, D, E, F and G. The Botulinum toxins are capable of binding at the presynaptic membrane of the motor nerve axon terminal via its heavy chain, followed by internalization of the light chain. The light chain reacts with cellular substrates consisting of SNAP-25 (immunotype A), synaptobrevin (immunotype B) and syntaxin (immunotype C). The cytoplasmic cellular substrates of the Botulinum toxins are integral in exocytosis of neurotransmitters which are coupled to motor nerve conduction. By virtue of the long duration of neuromuscular blockade which is induced upon administration of Botulinum toxin to a subject, catabolism occurs within the innervated striated muscle.
The lips of the mouth, via attendant muscular groups, are an important component of the muscles used in facial expression. The muscles of facial expression are also important in non-verbal communication. Lip position may indicate anger, frustration, threat, fear, determination while pondering, thinking or feeling uncertain. The face may show obvious muscular tension (i.e., with the lips held tightly together) or less noticeable tension (i.e., with the lips parted and slightly tightened). Hence, lip position and related deformities play an important role in communication, as well as external and self perception of appearance. Furthermore, deformity of the lip is instantly noticeable to patients and all who interact with those who may be afflicted with a lip deformity.
The anatomy of the lip is very complex. The inner surface of each lip is connected in the middle line to the corresponding gum by a fold of mucous membrane, the frenulum, the upper being the larger. The Orbicularis oris muscle is not a simple sphincter muscle like the Orbicularis oculi; it consists of numerous strata of muscular fibers surrounding the orifice of the mouth, but having different direction. The Orbicularis oris muscle consists partly of fibers derived from the other facial muscles which are inserted into the lips, and partly of fibers proper to the lips. Of the former, a considerable number are derived from the Buccinator and form the deeper stratum of the Orbicularis. Some of the Buccinator fibers, namely, those near the middle of the muscle, decussate at the angle of the mouth, those arising from the maxilla passing to the lower lip, and those from the mandible to the upper lip. The uppermost and lowermost fibers of the Buccinator pass across the lips from side to side without decussation. Superficial to this stratum is a second, formed on either side by the Caninus and Triangularis, which cross each other at the angle of the mouth; those from the Caninus passing to the lower lip, and those from the Triangularis to the upper lip, along which they run, to be inserted into the skin near the median line. In addition to these, there are fibers from the Quadratus labii superioris, the Zygomaticus, and the Quadratus labii inferioris; these intermingle with the transverse fibers above described, and have principally an oblique direction.
The proper fibers of the lips are oblique, and pass from the under surface of the skin to the mucous membrane, through the thickness of the lip. Finally, there are fibers by which the muscle is connected with the maxillae and the septum of the nose above and with the mandible below. In the upper lip these consist of two bands, lateral and medial, on either side of the middle line; the lateral band (m. incisivus labii superioris) arises from the alveolar border of the maxilla, opposite the lateral incisor tooth, and arching laterally and is continuous with the other muscles at the angle of the mouth; the medial band (m. nasolabialis) connects the upper lip to the back of the septum of the nose. The interval between the two medial bands corresponds with the depression, called the philtrum, seen on the lip beneath the septum of the nose. The additional fibers for the lower lip constitute a slip (m. incisivus labii inferioris) on either side of the middle line; this arises from the mandible, lateral to the Mentalis, and intermingles with the other muscles at the angle of the mouth.
The Risorius arises in the fascia over the Masseter and, passing horizontally forward, superficial to the Platysma, is inserted into the skin at the angle of the mouth. It is a narrow bundle of fibers, broadest at its origin, but varies much in its size and form. Variations of the zygomatic head of the Quadratus labii superioris and Risorius are frequently absent and more rarely the Zygomaticus. The Zygomaticus and Risorius may be doubled or the latter greatly enlarged or blended with the Platysma. The muscles in this group are all supplied by the facial nerve.
The Orbicularis oris muscle, in its ordinary action, effects the direct closure of the lips. By its deep fibers, assisted by the oblique ones, it closely applies the lips to the alveolar arch. The superficial part, consisting principally of the decussating fibers, brings the lips together and also protrudes them forward. The Buccinators compress the cheeks, so that, during the process of mastication, the food is kept under the immediate pressure of the teeth. When the cheeks have been previously distended with air, the Buccinator muscles expel it from between the lips, as in blowing a trumpet; hence the name (buccina, a trumpet). The Risorius retracts the angle of the mouth, and produces an unpleasant grinning expression.
Hypervolemic lips, commonly known as “fat lips” are considered disfiguring by some people. Often, when the deformity is present, hypervolemic lips are considered out of proportion with other facial structures. Excessive exposure of the mucous membrane (the red portion of the lip) is characteristic of the deformity. Some populations of individuals, such as African-Americans, may exhibit a higher prevalence of high lip volume. The deformity may also be individual and sometimes associated with upper jaw or maxillary protrusion, or “buck tooth” deformity. For aesthetic reasons, some wish reduction of lip prominence and seek facial, oral or plastic surgeons to achieve changes in lip dimension.
Hypervolemic lips are anatomically caused by one or more of the following structural deviations: 1) Excessive tone of lip retractor function of certain facial muscles such as levator labii superioris, zygomaticus major and minor, levator labii inferioris, platysma, and depressor labii inferioris; 2) Excessive prominence and development of orbicularis oris muscle; 3) Excessive non-muscular soft tissue volume within the lip itself.
The retractors of the lip can, in part, cause rotation of the mucous membrane with excessive resting tone or contraction, which is herein described as lip ectropion. The muscle fibers of the retractors often penetrate and intertwine with the fibers of the orbicularis ori muscle forming the bulk of the lip. Decrease in the retractor tone causes the lip's mucous membrane to roll inward giving the appearance of smaller lips. This phenomenon is seen in patients with facial nerve palsy unilaterally.
The present inventor has found that because Botulinum toxin can cause a decrease in the volume of muscle fibers and decreased facial tone, directed Botulinum toxin injection into the lip can effect reduction in lip volume. Directed injection into the retractors of the lip as well as the orbicularis ori muscle also serves to reduce lip ectropion and mucous membrane exposure. By altering the volume of muscle within the lip structure, the lip becomes slightly deflated, without changing other soft tissue structures. The methods described herein are reversible with time and the effect can be altered by changing injection placement and dose. The methods described herein eliminate the need for incisional surgery to achieve these results.
Currently, smaller lips associated with age-related changes, or hereditary predisposition, can be considered disfiguring and a commercial enterprise has emerged yielding over $100,00,000 per year using injectable fillers such as collagen and hyaluronidate to increase lip bulk. The notion of reducing excessive lip size and bulk with Botulinum toxin preparations represents the converse intervention to volume enhancement with fillers and gives the facial plastic surgeon a useful tool for treating these deformities.